This invention relates to can-type combustors of gas turbines and the like and, more particularly, to a combustor of the type described provided with fuel distributing and supplying means enabling stable combustion to be achieved over the entire operation range while reducing the amount of oxides of nitrogen produced in the combustor.
One type of fuel distributing and supplying means of the prior art used with a gas turbine is shown in FIG. 1, which includes a compressor 1 a combustor 2, a turbine 3, and a generator 50. Although only one combustor 2 is shown, there are provided a plurality of combustors 2 (6 to 12 in number) arranged annularly, with each combustor 2 having a fuel nozzle 4 connected to one end thereof. Each combustor 2 receives a supply of fuel from a master fuel conduit 7 by means of a fuel pump 9. The fuel from the master fuel conduit 7 is equally distributed to each combustor 2 by a fuel distributor 8 and delivered through a fuel conduit 14 mounting a check valve 16. The numeral 12 designates a fuel controller operative to effect control of the flow rate of the fuel by controlling a return adjusting valve 11 mounted on a bypass conduit 10 of the fuel pump 9 based on a flow-rate signal generated by a fuel flowmeter 13.
In the conventional fuel distributing and supplying means described hereinabove, the greater part of oxides of nitrogen are produced in the form of nitrogen monoxide in the combustion of the fuel in each combustor 2. The nitrogen oxide is exhausted through the turbine 3 to the atmosphere and combines with oxygen into nitrogen dioxide. In this reaction process, ozone and other oxydants are produced as by products under the influences of ultraviolet rays and certain types of hydrocarbons. These substances give rise to photochemical smog when the meteorological conditions are favorable, thereby adversely affecting the human body. For this reason, oxides of nitrogen have recently attracted attention as principal air polluting substances, along with oxides of sulfur and carbon monoxide.
Production of nitrogen monoxide in the aforesaid combustion process will be discussed in some detail. It is known that production of nitrogen monoxide is maximized in the theoretical mixture combustion range and reduced in amount in two combustion ranges above and below the theoretical mixture combustion range or the rich mixture combustion range in which air for combustion is in deficiency and the lean mixture combustion range wherein air for combustion is in excess. Thus, in order to reduce the amount of nitrogen oxide produced in a combustor, two combustion systems or a rich mixture combustion system and a lean mixture combustion system are available. When the former system is adopted, a problem will be raised with regard to the production of black soot due to incomplete combustion of fuel because of the lack of air. Meanwhile the latter system has been considered to be perferable because the presence of excess air does not produce the problem of black soot.
In the multiple can-type combustor for a gas turbine shown in FIG. 1, each combustor 2 is constructed to have a fuel nozzle 4. The adoption of the single fuel nozzle construction results in a wide variation (from 200 to about 50) in the air-fuel ratio from no load to high load condition, so that operation of the combustor 2 should be performed in this wide air-fuel ratio range. Because of this, if the combustor 2 is adjusted such that the aforementioned lean mixture combustion can be effected at high load, the air-fuel ratio will greatly rise at low load, with a result that combustion will become unstable at low load. Also, when each combustor is provided with one fuel nozzle, the rich mixture combustion or theoretical mixture combustion will take place in the vicinity of the fuel nozzle because air flow does not reach the fuel nozzle, even if air for combustion is introduced into the combustor in an amount which is on the excess side on an average. Thus, no great effects could be achieved in reducing the amount of oxides of nitrogen produced, although production of black soot can be avoided.